This invention relates to the fabrication of three-dimensional objects using extrusion-based layered manufacturing techniques. More particularly, the invention relates to forming three-dimensional objects by extruding solidifiable modeling material in a flowable state in three dimensions with respect to a base, wherein the modeling material is supplied in the form of a filament.
Three-dimensional models are used for functions including aesthetic judgments, proofing the mathematical CAD model, forming hard tooling, studying interference and space allocation, and testing functionality. Extrusion-based layered manufacturing machines build up three-dimensional models by extruding solidifiable modeling material from an extrusion head in a predetermined pattern, based upon design data provided from a computer aided design (CAD) system. A feedstock of either a liquid or solid modeling material is supplied to the extrusion head. One technique is to supply modeling material in the form of a filament strand. Where the feedstock of modeling material is in solid form, a liquifier brings the feedstock to a flowable temperature for deposition.
Examples of extrusion-based apparatus and methods for making three-dimensional objects are described in Valavaara U.S. Pat. No. 4,749,347, Crump U.S. Pat. No. 5,121,329, Crump U.S. Pat. No. 5,340,433, Crump et al. U.S. Pat. No. 5,503,785, Danforth, et al. U.S. Pat. No. 5,900,207, Batchelder, et al. U.S. Pat. No. 5,764,521, Dahlin, et al. U.S. Pat. No. 6,022,207, Stuffle et al. U.S. Pat. No. 6,067,480 and Batchelder, et al. U.S. Pat. No. 6,085,957, all of which are assigned to Stratasys, Inc., the assignee of the present invention.
In the modeling machines employing a filament feed, modeling material is loaded into the machine as a flexible filament wound on a supply reel, such as disclosed in U.S. Pat. No. 5,121,329. A solidifiable material which adheres to the previous layer with an adequate bond upon solidification and which can be supplied as a flexible filament is used as the modeling material. The extrusion head, which includes a liquifier and a dispensing nozzle, receives the filament, melts the filament in the liquifier, and extrudes molten modeling material from the nozzle onto a base contained within a build envelope. The modeling material is extruded layer-by-layer in areas defined from the CAD model. The material being extruded fuses to previously deposited material and solidifies to form a three-dimensional object resembling the CAD model. In building a model from a modeling material that thermally solidifies upon a drop in temperature, the build envelope is preferably a chamber which is heated to a temperature higher than the solidification temperature of the modeling material during deposition, and then gradually cooled to relieve stresses from the material. As disclosed in U.S. Pat. No. 5,866,058, this approach anneals stresses out of the model while is being built so that the finished model is stress free and has very little distortion.
In creating three-dimensional objects by depositing layers of solidifiable material, supporting layers or structures are built underneath overhanging portions or in cavities of objects under construction, which are not supported by the modeling material itself. For example, if the object is a model of the interior of a subterranean cave and the cave prototype is constructed from the floor towards the ceiling, then a stalactite will require a temporary support until the ceiling is completed. A support structure may be built utilizing the same deposition techniques and apparatus by which the modeling material is deposited. The apparatus, under appropriate software control, produces additional geometry acting as a support structure for the overhanging or free-space segments of the object being formed. Support material is deposited either from a separate dispensing head within the modeling apparatus, or by the same dispensing head that deposits modeling material. A support material is chosen that will adhere to the modeling material during construction, and that is removable from a completed object. Various combinations of modeling and support materials are known, such as are disclosed in U.S. Pat. No. 5,503,785.
In Stratasys FDM® three-dimensional modeling machines of the current art which embody a filament feed as disclosed in the above-referenced patents, a coil of modeling filament wrapped on a spool is loaded into the machine by mounting the spool onto a spindle. The filament is made of a thermoplastic or wax material. The user manually feeds a strand of the filament through a guide tube made of low friction material, unwinding filament from the spool until the filament strand reaches a pair of motor-driven feed rollers at the extrusion head. The filament strand is advanced by the feed rollers into a liquifier carried by the extrusion head. Inside the liquifier, the filament is heated to a flowable temperature. As the feed rollers continue to advance filament into the extrusion head, the force of the incoming filament strand extrudes the flowable material out from the dispensing nozzle where it is deposited onto a substrate removably mounted to a build platform. The flow rate of the material extruded from the nozzle is a function of the rate at which the filament is advanced to the head and the size of the dispensing nozzle orifice. A controller controls movement of the extrusion head in a horizontal x, y plane, controls movement of the build platform in a vertical z-direction, and controls the rate at which the feed rollers advance filament into the head. By controlling these processing variables in synchrony, the modeling material is deposited at a desired flow rate in “beads” or “roads” layer-by-layer in areas defined from the CAD model. The dispensed modeling material solidifies upon cooling, to create a three-dimensional solid object.
The Stratasys FDM® modeling machines use modeling filaments which are made from moisture sensitive materials, e.g., ABS thermoplastic. In order for the machines to function properly and to build accurate, robust models, the material must be kept dry. Therefore, filament spools for use in the machines are shipped, together with packets of desiccant, in moisture-impermeable packages. Each filament spool is to remain in its package until it is loaded into a modeling machine. The spindle onto which the spool is mounted is contained in a “drybox”, an area of the machine maintained at low humidity conditions. The user is instructed to place the desiccant packets packaged with the filament spool into the drybox, and to remove any desiccant packets placed in the machine with prior spools. After manually feeding the filament to the feed rollers, the user latches a door of the drybox and may instruct the machine to begin building a model. To unload the filament spool from the machine, the user manually winds the filament back onto the spool. U.S. Pat. No. 6,022,207 shows and describes a spool of the current art loaded into the drybox of a three-dimensional modeling machine.
Manually feeding filament to the head, as is presently done, can be tedious. Additionally, as a practical matter, users often leave old desiccant in the drybox and fail to replace it with new desiccant, allowing humidity in the drybox to reach unacceptable levels. Further, frequent switching of spools results in moisture-contaminated material. Opening and closing the drybox door allows humid air to get trapped inside of the sealed area. A partially used spool unloaded from the machine is exposed to moisture and becomes contaminated as well. These moisture contamination problems result in wasted material when the user switches the type or color of modeling material. Moreover, some materials desirable for use as modeling materials in the Stratasys FDM® machines are highly vulnerable to moisture and can get contaminated within minutes. The time during which the drybox door is opened for loading and unloading filament introduces a level of moisture into the drybox unacceptable for some desirable materials, limiting the choice of modeling materials for use in these machines.
It would be desirable to build models from moisture-sensitive materials by additive-process deposition methods without experiencing the negative effects of moisture contamination.